Flow restriction valves that convert fluid energy by pressure reduction are well known in the art. Such valves may comprise a simple design having a single stage for pressure reduction or a more complex design having multiple stages for gradual pressure reduction. Due to the noise level and the resulting wear of parts found in single stage reduction designs, multiple stage designs have become more common.
Multiple stage designs such as disclosed in U.S. Pat. No. 3,485,474, Apr. 8, 1968 to Baumann and U.S. Pat. No. 3,715,098, Feb. 6, 1973, to Baumann, present an incoming fluid with a tortuous path to gradually reduce the pressure in stages. An inlet and an outlet are typically separated by a passage that may be open or sealed shut. As the passage opens, the fluid encounters a first restricting structure altering the direction of flow, and then a second restricting structure and so on until the desired pressure drop has occurred. The repeated encounters with restricting structures create a sharply stepped pressure reduction.
While these designs generally function adequately, they are often complex structures requiring relatively expensive fabrication processes. Additionally, there is no simple way to clean the structures short of disassembly. These previous designs keep a fixed number of stages throttling at all times, reducing the capacity of the device. Thus, there is a need for a multistep trim design that allows a smooth pressure reduction, can be flushed without disassembly, is relatively inexpensive to manufacture and has the capability of providing a variation in stages with travel to provide large capacity ranges in a singe device.